1. Field of the Invention
This invention relates to a fire resistant resin for use as a binder in reinforced plastics and to such reinforced plastics as well as the method of making such resins and plastics.
2. Description of the Prior Art
It has been known to employ reinforced plastic materials such as fiberglass, for example, in a wide variety of environments including building products, transportation uses such as automobiles, planes and boats, as well as many other uses, such as air ducts, panels, doors and electrical conduits. The reinforcing material serves to enhance the strength of the plastic materials and the binders secure the material in the desired positions. A wide variety of reinforcing materials have been employed as reinforcing material. Examples of such materials are carbon fibers, glass fibers and flakes, glass or ceramic microspheres and a wide variety of synthetic materials in various forms including continuous fiber and chopped fiber.
Among the important considerations in resin binders used for such purposes are the desire to have effective resistance to both flame and smoke development, as well as maintaining the desired mechanical properties at elevated temperatures.
It has been known to employ a condensation product of resorcinol and formaldehyde resins in combination with cement in such resins. See U.S. Pat. No. 3,663,720. See also, U.S. Pat. No. 3,502,610.
Building codes and regulatory agencies specify low smoke density values for such thermosetting and thermoplastic materials that only a limited number of materials can be employed due to economic considerations. Further, increasingly tight restrictions have been imposed on emissions of styrene, a chemical generally deemed necessary in the industry. This is so as styrene is currently under investigation as being a possible carcinogen. While phenolic resins have been suggested as a safe alternative for fire retardant applications, one of the impediments to growth of use of such composites is the reluctance of fabricators to have the required acid catalyst present in the shop environment.
A serious problem with most fire-retardant resins is smoke emissions. It is currently believed that a high percentage of fatalities and fire are caused by smoke inhalation. Most fire retardant reinforced plastics tend to emit dense clouds of toxic and acutely irritating gases. Such smoke and gases can cause death or lung damage as a result of inhalation. They also can obstruct vision, thereby interfering with escape to safety and efforts of fire fighters. Further, damage to facilities including delicate electronic equipment can occur.
Most phenolic laminating resins rely upon acid catalysts or high temperature post-curing or both.
As formaldehyde has recently been classified as a carcinogen, one must carefully evaluate the level of paraformaldehyde disclosed in the prior art. It is important to reduce exposure of the laminating worker to a lower level of formaldehyde emissions.
U.S. Pat. No. 4,403,066 discloses the use of liquid phenol-formaldehyde resoles in reinforced composites such as those reinforced by glass fiber. One of the difficulties with the system taught in this patent is that it requires curing of the resin at an elevated temperature such as at about 80.degree. to 150.degree. C. and that it requires strongly acidic or alkaline conditions. See also, U.S. Pat. No. 4,433,129 which discloses hemi-formals of methylolated phenols including those made by reaction of paraformaldehyde with liquid phenol to produce hemi-formals of methylolated phenols.
U.S. Pat. No. 4,433,119 discloses liquid compositions of a hemi-formal phenol or methylolated phenols with polymers such as phenol-formaldehyde resoles, phenol-formaldehyde, novolak, as well as other materials. See also U.S. Pat. No. 4,430,473.
U.S. Pat. No. 4,053,447 discloses a resorcinol-modified phenolic resin which is said to be curable without the addition of heat. This disclosure requires the addition of paraformaldehyde powder to cure the resin mix.
It has been known to use resorcinol modified phenolic resins in the manufacture of glue laminated wooden structural members. Adaptation of this technology to reinforced plastics, has had limited success due to the relatively high level of non-reactive solvents formerly necessary to achieve low viscosity in conventional resin systems. The high solvent content of conventional "first generation resins" as well as the water formed in the phenolic condensation reaction contribute to crazing, porosity and poor corrosion resistance experienced in earlier resin systems.
In spite of the known prior art system, there remains a very real and substantial need for resin binder for reinforced plastics which will have the desired flame and smoke development resistant characteristics while being curable at room temperature and easy to manufacture and use.